Golf balls comprise, in general, three types. The first type is a wound ball wherein a vulcanized rubber thread is wound under tension around a solid or semi-solid core, and thereafter enclosed in a single or multi-layer covering of tough, protective material. A second type of golf ball is a one-piece ball formed from a solid mass of moldable resilient material which has been cured to develop the necessary degree of hardness to provide utility. One-piece molded balls do not have an enclosing cover. A third type of ball is a multi-piece (two or more piece) non-wound ball which includes a solid or liquid core of one or more layers and a cover having one or more layers formed over the core.
While for many years the wound ball satisfied the standards of both the U.S.G.A. and most golfers, it has several disadvantages. For example, a wound ball is difficult to manufacture due to the number of production steps required and the careful control which must be exercised in each stage of manufacture to achieve suitable roundness, velocity or rebound, "click", "feel" and the like. "Click" is the term applied to the sound produced by the ball when dropped on a hard surface or when struck with a golf club. "Feel" refers to how impact of the ball is transmitted through the club to the hands of the golfer. In addition, the balata cover material for the wound ball is susceptible to cutting when struck by a golf club.
The one-piece ball and the core for a multi-piece non-wound ball frequently are formed from a combination of materials such as polybutadiene, zinc diacrylate or zinc dimethacrylate, fillers and curing agents which are molded under high pressure and temperature to provide a ball of suitable hardness and resilience. One-piece balls are described, for example, in U.S. Pat. No. 3,313,545, U.S. Pat. No. 3,373,123 and U.S. Pat. No. 3,384,612. Multi-piece non-wound golf balls typically have a cover which contains a substantial quantity of ionomer. Useful ionomers include those sold by E. I. DuPont de Nemours Company under the name Surlyn.RTM. as well as those sold by Exxon under the name lotek.TM.. The use of ionomers in golf ball covers imparts toughness and cut resistance to the covers. It would be useful to develop golf ball covers which contain substantial quantities of non-ionomeric materials and which have the durability and other playability properties of ionomeric golf ball covers. Furthermore, it would be useful to develop durable one-piece golf balls having reduced quantities of polybutadiene.